Every day many practitioners, such as doctors, nurses, midwives and others, assist in the labor and delivery of infants. One problem that arises is inconsistency of cervical dilation readings or measurements between different practitioners, and inconsistency within cervical dilation measurements by the same practitioner. Because of the length of labor, the same practitioner usually does not follow the entire labor course of a given patient; therefore many practitioners are involved in the management of a laboring patient, leading to discrepancies and/or inconsistencies between cervical exams (especially at shift changes). Each of the practitioners may utilize different methods and techniques to obtain cervical dilation readings or measurements. Sometimes the same practitioner may obtain different readings when checking twice.
Inconsistency of cervical dilation readings may lead to problems managing labor. For example, accurate readings of progress of labor are essential because if the readings are inaccurate:                The actual present stage of labor is unknown.        The length of labor may be affected.        Practitioners may fail to offer necessary treatments.        Practitioners may recommend unnecessary treatments, including:                    Drugs            Maneuvers            Surgery                        
Different practitioners use different “metrics” to estimate cervical dilation, but these tactics are not standardized and there is no testing of accuracy or precision of the measurements. Generally, a practitioner will insert two fingers into the vagina and feel the cervix. The practitioner will then estimate, by feel, the magnitude of dilation of the cervix. Therefore, the measurement is subjective. In addition, there is no consistent training provided to student practitioners (MDs/midwives/nurses) to standardize the approach.
Studies have been done to determine accuracy of practitioners at determining cervical dilation. One study was designed to measure precision (variation within and between observers) and accuracy of expert cervical assessment against an objective standard using carefully constructed simulators. No examiner achieved correct assessment in every case tested. The assessment of cervical dilation was exactly right in only 175 of 360 cases (48.6%). (Tuffnel et al, Simulation of cervical changes in labour: reproducibility of expert assessment, 1989).
In another study, polyvinyl chloride pipes 1 to 10 cm in diameter were mounted in cardboard boxes and used to simulate cervical examinations. The boxes were designed so that the examiner had to rely solely on proprioception to determine the inner diameter. In the results, a total of 1574 simulated cervical diameter measurements were obtained from 102 examiners in a two-part study. The overall accuracy for determining the exact diameter was 56.3% and intraobserver variability for a given diameter measurement was 52.1%. (Phelps, Accuracy And Intraobserver Variability Of Simulated Cervical Dilatation Measurements, 1995).
While the above studies used simulators, another study was done to determine accuracy in estimation of cervical dilation during the active phase of labor in vivo and to identify independent predictors of inaccuracy. Examinations were performed on 508 women. The researcher and clinicians agreed on the dilation in 250 instances (49.2%) and differed by 2 cm or more in 56 cases (11.0%). (E J Buchmann the Accuracy of cervical assessment in the active phase of labour, 2007).
As is evident, the practitioners differ about half the time in their measurements of cervical dilation. Inaccuracy and imprecision may negatively impact patient care related to treatment and management decisions based on cervical dilation. “Labour management is based on the assessment of the cervix. Decisions to augment labour or even carry out caesarean section are heavily influenced by the progress of labour, and assessment of progress is based on cervical dilation. Variation between observers is therefore important when care is shared and shift changes.” (Tufihel et al, Simulation of cervical changes in labour: reproducibility of expert assessment, 1989).
An incorrect cervical dilation measurement may also increase the risk of the practitioner augmenting labor, which can pose risks to both the mother and the baby. Augmenting labor increases the risk of several complications, including:                Cesarean section.        Fetal heart rate decelerations which indicate decreased oxygen delivery to the fetus.        Post partum hemorrhage.        Blood transfusion and related risks.        Infection.        Uterine rupture.        
Tools have been developed or examined to assist the practitioner in determining cervical dilation. Examples of such tools include a translabial 3-dimensional (3D) ultrasonogram, mechanical calipers, electrical displacement transducers clipped to opposite sides of the cervical rim, and a caliper-like cervimeter with leaf spring arms that coil against the outer rim of the cervix for measurement.
Each of these tools was found to be unsatisfactory because they are complex, expensive, inaccurate, increase the risk of infection, may cause patient discomfort, and are difficult to integrate into clinical practice. In addition, they can: distort the cervix (introducing measurement error), cause cervical trauma, and are poorly reproducible. They are also time consuming for the practitioner and require substantial training to develop proficiency. Some protrude from the vagina, interfering with vaginal exams and increasing infection risk.
“The determination of cervical dilatation is necessary in the management of labor. The rate of cervical dilatation is used to define the effectiveness of uterine contractions and the adequacy of labor. Lack of progression of cervical dilatation influences the decision to augment labor or to perform a cesarean section. Therefore it is very important that the estimate of cervical dilatation be reasonably close to the true cervical diameter when there is more than one examiner involved in the management of a laboring patient. The digital examination remains the “gold standard” for evaluation of the cervix in pregnancy; however, it has inherent variability.” (Phelps, Accuracy And Intraobserver Variability Of Simulated Cervical Dilatation Measurements, 1995).
Thus there is a need for methods and apparatus for accurate and consistent cervical dilation measurements or readings during labor for practitioners, and between different practitioners with the same patient during labor, that avoid the problems mentioned above.